Auto-lock old issues.

.github/workflows/autolock.yaml

@@ -0,0 +1,28 @@
+# Locks closed issues and pull requests after a period of inactivity, to
+# prevent spam and noise.
+name: Autolock
+"on":
+  schedule:
+    # Run weekly, every Monday at 8:43.
+    - cron: "43 8 * * 1"
+
+jobs:
+  lock:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/lock-threads@v2.0.1
+        with:
+          github-token: ${{ github.token }}
+          # Lock down after 3 months.
+          issue-lock-inactive-days: '90'
+          issue-lock-reason: 'resolved'
+          issue-lock-comment: >
+            This issue has been automatically locked since there
+            has not been any recent activity after it was closed.
+            Please open a new issue for related bugs.
+          pr-lock-inactive-days: '90'
+          pr-lock-reason: 'resolved'
+          pr-lock-comment: >
+            This pull request has been automatically locked since there
+            has not been any recent activity after it was closed.
+            Please open a new issue for related bugs.